CO₂ Capacity and Heat of Sorption on a Polyethylenimine-Impregnated Silica under Equilibrium and Transient Sorption Conditions

Amine-based solid sorbents represent promising replacements for aqueous alkanolamines for CO₂ capture because they reduce significantly the sorbent regeneration energy and avoid instrument corrosion encountered with aqueous amine solutions. CO₂ capture by solid amine sorbents is often achieved by pressure-temperature-swing adsorption (PTSA) technology, which selectively sorbs CO₂ from a gas mixture and desorbs concentrated CO₂ by pressure swing and/or heating. CO₂ capacity and heat of sorption on different types of amine-based solids have been evaluated predominantly under equilibrium conditions using thermogravimetric analysis (TGA), with emphasis on parametric studies of temperature, amine loadings, and supporting substrates on CO₂ sorption kinetics and capacity. Owing to differences in the configuration between a TGA apparatus and a PTSA column, CO₂ capacity and heat of sorption may vary under transient sorption condition versus equilibrium sorption condition. In this work, we constructed a laboratory-scale breakthrough reactor (BTR) to simulate the industrial PTSA process, evaluated CO₂ capacity and heat of sorption at different temperatures under transient sorption conditions, and compared these values with equilibrium values determined by volumetric sorption analysis. We found that the temperature effects on CO₂ capacity and the heat of sorption differ under the two sorption modes. CO₂ capacity and heat of sorption data not only provide useful information for the design of sorption and regeneration processes, but also enable spatiotemporal modeling of the CO₂ sorption process in a packed bed.